Supersonic diffuser and control therefor



Jan. 15, 1963 R. M. STEVENS 7 SUPERSONIC DIFFUSER AND CONTROL THEREFOR Filed Dec. 29, 1948 2 Sheets-Sheet 1 FIG. I

1 0 L2 L4 L6 L8 2.0 2.2 2.4 2.6 2.8 3.0 MACH NO.

STRAIN GAG ES 23 MOTORS\23-" INVENTOR. ROBERT M. STEVENS WWW ATTORNEY.

Jan. 15, 1963 R. M. STEVENS SUPERSONIC DIFFUSER AND CONTROL THEREFOR Filed Dec. 29, 1948 2 Sheets-Sheet 2 in T 2 Q Q" I 0 cu I N 9' I! I v a T I 4 \I N X a n I n N INVENTOR. ROBERT M. STEVENS 6* Eco/w. was" ATTORNEY.

3,073,109 SUPERSONIC DIFFUSER AND CONTROL THEREFQR Robert M. Stevens, Columbus, Ohio, assignor to Curtiss- Wright Corporation, a corporation of Delaware Filed Dec. 29, 1948, Ser. No. 67,899 26 Claims. (Cl. 69-356) The present invention relates to a diffuser for ram jet engines and the like, for converting dynamic head of fluid entering at supersonic velocity into static head.

An ideal diffuser for this purpose would be of convergent-divergent configuration, so proportioned that air or other gas entering at supersonic speed would be decelerated to exactly the speed of sound as it passed through the convergent section, and then, with shock-free flow, further decelerated as it passed through the divergent section, thus reaching efficiently the desired condition of low velocity and high static pressure at the diffuser outlet, which, as applied to a ram jet engine, may be the forward portion of the combustion chamber. With this ideal arrangement there would be maximum compression of the entering air for a given decrease in its velocity. However this ideal is difficult, if not impossible, to achieve in practice since any relative change of the pressures at the diffuser inlet and outlet, or change of velocity or temperature of the entering air, will result either in the formation of a shock wave across the fluid stream at some point forward or aft of the diffuser throat, or in supersonic flow entirely through the engine. In case of shock in advance of the diffuser throat a bow shock wave will occur across or ahead of the mouth of the diffuser, so that there will be an accelerating subsonic flow through the convergent section of the diffuser, instead of the desired decelerating supersonic flow. In case the shock is across the divergent section of the diffuser there is a decrease in compression efficiency due to the entropy rise incident to shock, the total pressure of the air stream emerging from the shock being less than that entering the shock.

In order to allow the engine to operate efficiently throughout a reasonably wide range of temperatures and supersonic velocities it is necessary, first, to vary the effective ratio of diffuser inlet area to diffuser throat area so that the velocity at the throat is only slightly above the speed of sound, making possible the formation of a shock wave aft of the throat; and, second, to adjust the pressure gradient through the engine so as to maintain the shock United States atent O wave across the divergent section of the diffser only slightly downstream from the throat. In this way there will be a minimum loss of usable energy.

By the present invention the effective area relationship between diffuser mouth and throat is accomplished by spilling a portion of the entering air from the convergent section of the diffuser into the surrounding air-stream, preferably in such manner that the spilled air retains a substantial portion of its kinetic energy; and the shock wave is maintained in the desired position within the divergent diffuser section by spilling air from the outlet of the diffuser, thereby varying the effective ratio of diffuser entrance area to diffuser outlet area. I

According to the invention an outer diffuser passage of convergent-divergent form is provided, and arranged concentrically therein for fore-and-aft movement is a tube which also is of convergent-divergent form and whose entrance area is less than that of the outer passage. In its rearmost position of fore-and-aft movement the convergent section of the tube forms a continuation of the convergent section of the outer passage, so that all entering air passes through the tube; and in any other position of the tube an annular spillway is provided between the outer passage walls and the outer surface of the tube, whereby ice a portion of the air entering the diffuser is diverted and does not pass through the tube. The farther forward the tube moves the greater the area of the spillway and the larger the proportion of spilled air. The forward movement of the tube also opens an annular spillway at the diffuser outlet, so that another fraction of the entering air is diverted to the outside airstream and does not enter the combustion chamber.

The diverted air is discharged in such manner that it retains much of its momentum. This, in the case of air diverted from the diffuser throat, is accomplished by providing an annular spillage outlet of variable area so that the velocity of flow from the spillage outlet may correspond as closely as possible to that of the surrounding airstream which it is entering. Such variation of spillage outlet area is conveniently accomplished by movement of a sleeve valve.

The invention further provides means for effecting adjustment of the tube, and also of the spillage outlet valve, automatically in response to variations in flow through the diffuser to the end that shock across the stream is maintained at the desired location slightly downstream from the diffuser throat. The adjusting means include a reversible motor for shifting the tube and the outlet spillage valve fore-and-aft, and further include control means for the motor comprising elements that are responsive to changes in the ratio of pressure at the throat to pressure at the diffuser outlet.

The foregoging and other objects and advantages of the I invention will become apparent from the following description made in connection with the accompanying drawings wherein:

. FIG. 1 is a graph showing the desired relationship of effective areas at the diffuser inlet, diffuser throat and diffuser outlet, for a ram jet engine chosen as an example;

FIG. 2 is a longitudinal sectional view of the present diffuser as applied to one form of ram jet engine;

FIG. 3 is a cross sectional view taken along line 33, of FIG. 2; and,

FIG. 4 is a diagram of the system for automatically adjusting the diffuser shown in FIGS. 2 and 3 in response to pressure changes.

The general way in which the area relationships of fixed configuration diffusers of the convergent-divergent type should differ for entering air-streams of different Mach numbers in order to provide maximum compression efliciency is shown graphically in FIG. 1. The ram jet engine chosen for this illustration is one having a constant crosssectional area from diffuser outlet to exhaust orifice, and

designed to operate with a constant fuel-air ratio and with an exhaust velocity the speed of sound. For an entering air-stream at three times sonic speed, or M=3, the ratio of diffuser inlet area to diffuser outlet area should be about 1.61 and the ratio of throat area to outlet area about 0.38 in order to cause the internal airstream to pass from supersonic to subsonic velocity without shock.

As shown by the graph these-ratios should be smaller in diffusers designed for lower entering air velocities, until for M=l both ratios should be about 0.260. In this last case of course the diffuser would have no convergent,

section at all.

maximum design speed of the particular engine, but the effective area is reduced to the values necessary for lower airspeeds by spilling a portion of the entering air before it reaches the diffuser throat. Similarly the actual throat area remains constant at the value for maximum'design speed, but its effective value is also reduced to the degree necessary for a lower airspeed by spilling air from the position,- shown in broken lines designated 15.

diflus'e'r betweenthe throat and the engine combustion chamber. 7

In FIGS. 2 and 3 the diifuseris indicated generally at 10, the combustion section at 11, and tail pipe at 12. The diffuser serves to reduce the velocity of entering air and compress it; in the combustion section the temperature of the compressed air is increased by the burning of fuel which is supplied and ignited by suitable means (not shown); and the heatedair, including combustion pro ducts, is accelerated by thermal expansion to a velocity much higher than at the diffuser entrance and then exhausts into the atmosphere through the outlet orifice of Q tailpipe 12. Y

The difiuser includes an annular member 13 supported by arms 14-which extend forwardlyfrom the body 11, and an inner tubular member 15 mounted for fore-and aft movement relative to parts 11 and 13. The inner surface of annulus 13 provides a forward section 16 which converges from the entrance whose area is designated A to the throat or most constricted portion, and further provides an aft passage section 18 which diverges rearwardly from the throat 17 to the trailing 'edge of the annulus which is spaced from the body 11.

The tube 15 is also of convergent-divergent form, its

" forward section converging from a mouth whose area is less than that of the entrance of the outer tube 13 to a throat whose area is designated A The rear section of tube 15 divergesfrom A to its trailing edge which is adapted toclose into nested relation withv the beveled forward edge of bodyll when the tube is in its rearmost in this position the convergent section of the tube formsa continuation ofconvergent section 16' of the outer passage.

Tube 15 has forwardly extending support rods 19 mounted for fore-and-aft sliding movement in bearings 20 formed on annulus 13. The forward end of each support rod is screw threaded into a shaft 21 whose outer surface is also screw threaded for engagement with a nut 22. Shafts 21 are driven by reversible electric motors 23' to effect fore-and-aft adjustment of tube 15 and also of a sleeve valve 24 which telescopes on the outer surface ofannulus 13 and is connected by arms 25 to the nuts 22.

Extending across the tube 15 is a strut 26 for supporting a total head tube 27 whose mouth is approximately at the throat of the tube. Extending in similar fashion across body 11 is a strut 28 supporting a total head tube 29. having its mouth adjacent the outlet end of the diffuser section. The area A of the diffuser outlet represents approximately thelocation in the system where the velocity will 'be lowest and the static pressure highest. The tubes 27 and 29 extend to motor cntrol means which may be. housed in the annulus 13. As shown by broken lines 27'. and 29" the tubes 27 and 2? may extend respectively through supports'19 and 14-. The motor control means include a three position polarized relay 31 for directly controlling the motors and pressure responsive resistance devices 32 and 33 shown diagrammatically in FIG. 4 for controlling 'the relay.

As shown in FIG. 4 the device 32 comprises a container whose interior is divided by a diaphragm 34 to pro-. vide a sealed chamber 35 and a chamber 36 connected with total head tube 27. An electrical resistance strain gage 37 is secured to the diaphragm 34 in such manner that its resistance will increase with increase of pressure in chamber 36. Gage 37 forms one arm of a Wheatstone bridge circuit, being connected across terminals 38 and 39 of the later. Similarly a straingage 40, electrically connected across terminals 39 and 41 of the bridge, is secured to a diaphragm 42 which separates chambers '43 and 44-in device 33, so that its, resistance increases with rise of pressure in chamber 44, the latter being connected to total head tube 29 and chamber 43 being sealed. 7 The bridge circuit further comprises a fixed resistor 45 connected across terminals 41 and 46, and a variable resistor 47 connected across terminals 33 and 46. A

source of direct current 48 connects input terminals 39 and 46 of the bridge circuit, while the polarized relay 31 is connected between the bridge output terminals 38 and 41.

The movable contact 49 of the polarized relay is arranged to close against either fixed contact 5%) or fixed contact 51 to close a circuit from a source of direct current 52 to forward winding 53 or reverse winding 54 of the motors 23 (only one of which is shown in FIG. 4). A normally closed switch S5 is arranged in the path of an extension on nut 22 to open the circuit through forward motor winding 53 when the tube 15 and valve 24 have been operated to their most forward position (shown in FIG; 1). Similarly a normally closed switchfid is arranged in the path of arm 25 to be opened thereby for breaking the circuit through reverse winding 54 when the valve 24 and tube 15 are moved to theirrearmost positions. 7

During operation of the jet engine the motors 23 serve to shift the tube 15 fore-and-aft in accordance with the pressures within tubes 27 and 29. The resistor '47 is so adjusted that the-bridge circuit is in balance, to the end that relay 31 and motor 23 are de-energized, when the pressure in tube 29 is higher than that in tube 27 by an amount referred to in the following paragraph.

.When a shock forms across tube 15 at the location designated A in FIG. 2, the velocity at A must be sonic or supersonic and the airstream between A and A is accelerating. A bow shock wave will extend across the mouth of total head tube 27 and a drop in total head will occur across this bow wave. However, since the velocity immediately upstream of A is higher than at A there will be a greater pressure drop across the shock at A.,, than across this how wave, and hence the pressure within tube 29 will be less than that in tube 27. The resistance of element 47 is so adjusted that the bridge circuit is in balance, and relay 31 is de-energized, when this pressure diiference exists. Accordingly when the shock wave across the divergent portion of tube15 occurs forwardly of A so that there is a smaller diiference between the pressures within tubes 27 and 29, the bridge is unbalanced in a direction to energize relay 31 to close contacts 49 and 50 which in turn causes the circuit through forward motor windings 53 to be established; and when the shock wave moves aft of A a larger pressure difference will exist, unbalancing the bridge circuit in the opposite direction and thereby causing the reverse motor windings 54 to be closed at 51.

When the velocity at the diffuser throat is subsonic,

substantially equal pressures will exist in the total head.

tubes 27 and 29. Accordingly as the engine is brought from a standstill to its operating airspeed the bridge circuit will remain unbalanced in the direction which will cause themotors to maintain the tube 15 in its most forward position, with both spillage passages fully opened, until a velocity is reached that is sufiiciently high to cause a shock to form in the divergent portion of tube 17 and move aft to a position slightly downstream of A This condition indicates that the flow at A is above the intended supersonic velocity at that point and also that the back pressure at section 11 is too low for the particular airspeed of the engine, and it will result in unbalancing the bridge in the opposite direction This will cause the motors to shift tube 15 rearwardly, decreasing both spillage areas, until the proper pressure differential between tubes 27 and 29 again prevails, at which time the relay 31 will be de-energized discontinuing the motor operation. f r

In this way, as the velocity or temperature of the entering air changes within the operating range of the engine,

resulting in a different relation between velocity of enter number, exceeds that at which the tube is moved to its most rearward position, the diffuser in effect becomes a fixed diffuser having the configuration shown by dotted lines 15' in FIG. 1.

As the tube 15 moves fore-and-aft to vary the proportion of entering air spilled from the diffuser throat, the sleeve valve 24 will simultaneously be adjusted fore-andaft to vary the size of the spillage outlet. In this way the velocity at that outlet'is made to correspond as closely as possible to the velocity of the airstream outside of the engine, so that as much as possible of the kinetic energy of the spilled air is retained.

It will be understood from reference to FIG. 1 that the effective inlet area must increase with Mach number increase much more rapidly than the effective throat area. Accordingly the spillway area at the trailing edge of tube 15 must be made to decrease with airspeed increase at a much more rapid rate than the area of the spillway at the leading edge of the tube. The desired relative change in spillway areas can be obtained in the design of the diffuser by varying the slopes of the convergent and divergent walls of the outer passage and tube 15 whose relative positions determine the spillway areas.

The invention has been specifically described herein as applied to a ram jet engine. However, it will be understood that it is also applicable to apparatus of other kinds, one example being a supersonic wind tunnel, in which it is desired to convert dynamic head of a supersonic fiow into static head.

It will also be understood that various changes may be made in the diffuser design and construction within the purview of the invention; that the foregoing detailed description is made by way of explanation and illustration and not with any intention to limit the invention; and that the scope of the invention is intended to be limited only as required by the appended claims.

I claim as my invention:

1. A diffuser for reducing the velocity of a fluid stream from a supersonic velocity at the diffuser entrance to a subsonic velocity at the entrance of a conduit, comprising a convergent-divergent passageway with the trailing edge of the divergent section thereof spaced from said entrance, a tube of convergent-divergent form arranged for longitudinal movement between first and second positions within said passageway, said tube when in the first position having the leading edge of the convergent section thereof substantially at the throat of the passageway whereby the convergent section of the tube forms'a rearward continuation of the convergent section of the passageway, and said tube when in the first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when in the second position having the leading edge of the convergent section thereof spaced from the throat of the passageway to provide a first spillway between the divergent sections of the tube and passageway, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide therebetween a second spillway, a slide valve arranged for longitudinal movement for varying the out.- let area of said first spillway, operating means for moving the tube and for simultaneously moving said slide valve to open and close the latter as the tube is moved toward and away from said second position, and pressure responsive means for controlling said operating means, said means effecting movement of the tube toward said first position'when the ratio of total head at the tube throat to total head at the tube outlet is above a predetermined value and for elfecting movement of the tube toward said second position when said ratio is below said value.

2. A diffuser for reducing the velocity of a fiuid stream from a supersonic velocity at the diffuser entrance to a subsonic velocity at the entrance of a conduit, comprising a convergent-divergent passageway with the trailing edge within said passageway, said tube when in the first position having the leading edge of the convergent section thereof adjacent the-wall of the convergent section of the passageway whereby the convergent section of the tube forms a rearward continuation of the convergent section of the passageway, and said tube when in the first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when inthe second position having the leading edge of I the convergent section thereof spaced from the wall of the passageway to provide a first spillway between the divergent sections of the tube and passageway, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide therebetween a second spillway, operating means for moving the tube and pressure responsive means for controlling said operating means, said means efiecting movement of the tube toward said first position when the ratio of total head at the tube throat to total head at the tube outlet is above a predetermined value and for effecting movement of the tube toward said second position when said ratio is below said value.

3. A diffuser for reducing the velocity of a fluid stream from a supersonic velocity at the diffuser entrance to a subsonic velocity at the entrance of a conduit, comprising a convergent-divergent passageway with the trailing edge of the divergent section thereof spaced from said entrance, a tube of convergent-divergent form arranged for longitudinal movement between first and second positions within said passageway, said tube when in the first position having the leading edge of the convergent section thereof adjacent the wall of the convergent section of the passageway whereby the convergent section of the tube forms a rearward continuation of the convergent section of the passageway, and said tube when in the first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when in the second position having the leading edge of the convergent section thereof spaced from the wall of the passageway to provide a first spillway between the divergent sections of the tube and passageway, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide therebetween a second spillway, a slide valve arranged for longitudinal movement for varying the outlet area of said first spillway, and operating means for moving the tube and for simultaneously moving said slide valve to open and close the latter respectively as the tube is moved toward and away from said second position.

4. A diffuser for reducing the velocity of a fluid stream from a supersonic velocity at the diifuser entrance to a subsonic velocity at the entrance of a conduit, comprising a convergent-divergent passageway with the trailing edge of the divergent section thereof spaced from said entrance, a tube of convergent-divergent form arranged for longitudinal movement between first'and second positions within said passageway, said tube when in the first position having the leading edge of the convergent section thereof adjacent the wall of the convergent section of the passageway whereby the convergent section of the tube forms a rearward continuation of the convergent section of the passageway, and said tube when in the first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when in the second position having the leading edge of the convergent section thereof spaced from the wall of the passageway to provide a first spillway between the divergent sections of the tube and of the passageway, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide therebetween a second spillway.

5. A diffuser for reducing the velocity of a fluid stream from a supersonic to a subsonic velocity at the entrance of a conduit, comprising a pasageway having a'convergent sectionfor reducing the velocity of entering fluid, the trailingedge of said passageway being spaced from said entrance, a tube ofconvergent-divergent form arranged for longitudinal movement between first and second limit positions relative to said passageway, the convergent section of said tube when in the first position constituting a rearward continuation of said convergent section of the pars sa'geway, and saidtube when in the first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when in the second position having'the leading edge of the. convergent section thereof spaced fromthe wall'of said convergent section. of the passageway to provide a. first spillway therebetween, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide a second spillwaytherebetween, operating means for moving the tube, and pressure responsive means for controlling said operating means, said means effecting movement of the tube toward said first position when the ratio of total head at the tube throat to total head at the tube outlet. is above a predeermined value and for effecting movement of the tube toward said second position when said ratio is below said value.

6. A diffuser for reducing the velocity of a fluid stream from a supersonic. to a subsonic velocity at the entrance of a conduit, comprising a pasageway having a convergent section for initially reducing the velocity of entering fluid,

the trailing edge of said passageway being spaced from said entrance, a tube of convergent-divergent form arranged for longitudinal movement between first and second limit positions relative to said passageway, said tube when ,inthe first position having the convergent section thereofconstituting a rearward continuation of said convergentfsection of the passageway, and said tube when in the t first position having the trailing edge thereof at the entrance of the conduit whereby the divergent section of the tube forms a forward continuation of the conduit, said tube when in the second position having the leading edge of the convergent section thereof spaced from the wall of said convergent section of the passageway to provide a first spillway, and said tube when in said second position having the trailing edge of the divergent section thereof spaced from the entrance of said conduit to provide a second spillway, whereby as the tube is moved from said first position to said second position the effective entrance area of the diffuser is reduced relative to the throat area of the tube, and the effective entrance area of the diffuser and effective throat area of said tube are both reduced relative to the area at the entrance of said conduit.

7. In a ram jet engine, a diffuser providing a convergentdivergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser :at asupersonic velocity to a subsonic velocity at saidcombustion' chamber, said diffuser having a first spillway leading from the convergent section thereof and a second spillway from the divergent section thereof, cp-

' erating means for adjusting said diffuser to simultaneously increase or decrease the areas of said spillways, and means responsive to pressure changes within said engine for controlling said operating means for maintaining the transition from supersonic to subsonicfiow at a location in said divergent section near said throat.

8. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to provide a substantially closed passage from the diffuser entrance to the combustion chamber or to provide a variable area first spillway leading from the convergent section of the passage and a second variable area spillway from the divergent section thereof, operating means for adjusting said diffuser parts to simultaneously increase or decrease the areas of said spillways, and means response to relative pressure changes within said engine at the diffuser throat and aft thereof for controlling said operating means for maintaining the transition from supersonic to subsonic fiow at a location in said divergent section near said throat.

9. In a ram jet engine, a multi-part diifuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to provide a substantially closed passage from the diffuser entrance to the combustion chamber or to provide a variable area first spillway leading from the convergent section of the passage and a second variable area spillway from the divergent section thereof, operating mean-s for adjusting said diffuser parts to simultaneously increase or decrease the areas of said spillways, and means responsive to pressure changes within said engine for controlling said operating means for maintaining the transition from supersonic to subsonic flow at a location in said divergent section near said throat.

10. in a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to provide a substantially closed passage from the diffuser entrance to the combustion chamber or to provide a variable area first spillway leading from the convergent section of the passage and a variable area second spillway from the divergent section thereof, and operating means for adjusting said diffuser parts to simultaneously increase or decrease the areas of said spfllways, whereby the velocity at said throat may be maintained above the speed of sound and the transition from supersonic to subsonic flow maintained at a location in said divergent section near said throat.

11. A multi-part diffuser providing a convergent-divergent passage leading to a fiuid conduit for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said conduit, the parts of the diffuser being relatively movable to provide a substantially closed passage from the diffuser entrance to said conduit or a variable area first spillway leading from the convergent section of the passage and a second spillway from the divergent section thereof, operating means for adjusting said diffuser parts to simultaneously increase or decrease the areas of said spillways, whereby the transition from supersonic to subsonic flow may be caused to occur from a velocity only slightly above the speed of sound at a point in said divergent section near the throat of the passage.

12. In a ram jet engine, a rnulti-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to open or close a spillway leading from the convergent section of the passage, operating means for adjusting said diffuser parts to close the spillway or vary the'opening thereof, and means responsive to pressure changes within said engine for controlling said operating means for maintaining the flow at the diffuser throat at only slightly above sonic velocity, whereby substantial deceleration of the flow may occur in the divergent section of the passage.

13. In a ram jet engine, amulti-part' diffuser providing a convergent-divergent passage leading-to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to open or close a spillway leading from the convergent section of the passage, and operating means for adjusting said diffuser parts to close the spillway or vary the opening thereof.

14. Amulti-part diffuser providing a convergent-divergent passage leading to a conduit for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said conduit, the parts of said diffuser being relatively movable to open or close a spillway leading from the convergent section of the passage, and operating means for adjusting said diffuser parts to close the spillway or vary the opening thereof, whereby the flow at the diffuser throat may be maintained at only slightly above sonic velocity to enable a substantial deceleration of the flow to occur in the divergent section of the passage.

15. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine com bustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to open or close a spillway leading from the divergent section of the passage, operating means for adjusting said diffuser parts to close the spillway or vary the opening thereof, and means responsive to pressure changes within said engine for controlling said operating means for maintaining the transition from supersonic to subsonic flow in the divergent section of the passage near the throat whereby substantial deceleration of the flow may occur in the divergent section of the passage.

16. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to open or close a spillway leading from the divergent section of the passage, and operating means for adjusting said diffuser parts to close the spillway or vary the opening thereof, whereby the transition from supersonic to subsonic flow may be maintained in the divergent section of the passage near the throat to provide for substantial deceleration of the flow in the divergent section of the passage.

17. A multi-part diffuser providing a convergent-divergent passage leading to a conduit for reducing the velocity of a fluid stream entering the the diffuser at a supersonic velocity to a subsonic velocity at said conduit, the parts of said diffuser being relatively movable to open or close a spillway leading from the divergent section of the passage, and operating means for adusting said diffuser parts to close the spillway or vary the opening thereof, whereby the transition from supersonic to subsonic flow may be maintained in the divergent section of the passage near the throat to provide for substantial deceleration of the flow in the divergent section of the passage.

18. In a ram jet engine, a multi-part diffuser providing a convergent-divergentpassage leading to the engine combustion chamber for reducing the velocity of fluid entering the diffuser to a speed above the speed of sound in the convergent section and for further reducing the velocity to a speed below the speed of sound in the divergent section, the parts of the diffuser being adjustable to vary the ratio of effective diffuser entrance area to effective diffuser throat area and to simultaneously vary the ratio of effective throat area to the combustion chamber area, whereby the flow may be maintained at only slightly above sonic speed at the throat of the difluser passage and the transition from supersonic to subsonic flow may be maintained in the divergent section near said throat.

19. A multi-part diffuser providing a convergent-divergent passage leading to a conduit for reducing the velocity of fluid entering the diffuser to a speed above the speed of sound in the convergent section and for further reducing the velocity to below the speed of sound in the divergent section, the parts of the diffuser being adjustable to vary the ratio of effective diffuser area to effective diffuser throat area and to simultaneously vary the ratio of effective throat area to the conduit area, whereby the flow may be adjusted to only slightly above sonic speed at the throat and the transition from supersonic to subsonic flow may be maintained in the divergent section near said throat.

20. In a device having an entrance passage including a divergent section for reducing the velocity of a fluid stream entering said section at a low supersonic velocity to a subsonic velocity at the outlet of said section, means for adjusting the device to maintain the locus of transition from supersonic to subsonic flow in said divergent section near the entrance thereof, a first total head tube opening into the passage upstream from said locus and a second total head tube opening into said passage downstream from said locus, and means responsive to the pressures prevailing in said total head tubes for operating said adjusting means.

21. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combusion chamber, the parts of said diffuser being relatively movable to provide a variable area first spillway leading from the convergent section of the passage and a variable area second spillway from the divergent section thereof, and operating means for adjusting said difiuser parts to simultaneously increase or decrease the areas of said spillways, whereby the velocity at said throat may be maintained above the speed of sound and the transition from supersonic to subsonic flow maintained at a location in said divergent section near said throat.

22. A multi-part diffuser providing a convergent-divergent passage leading to a fluid conduit for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said conduit, the parts of the diffuser being relatively movable to provide a variable area first spillway leading from the convergent section of the passage and a second spillway from the divergent section thereof, operating means for adjusting said diffuser parts to simultaneously increase or decrease the areas of said spillways, whereby the transition from supersonic to subsonic flow may be caused to occur from a velocity only slightly above the speed of sound at a point in said divergent section near the throat of the passage.

23. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine combustion chamber for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said combusion chamber, said diffuser further providing a spillway leading from the convergent section of the passage, the parts of the diffuser being relatively movable to vary the area of said spillway, and operating means for adjusting said diffuser parts to vary said area.

24. A multi-part diffuser providing a convergent-divergent passage leading to a conduit for reducing the velocity of a fluid stream entering the diffuser at a supersonic velocity to a subsonic velocity at said conduit, the parts of said diffuser being relatively movable to provide a variable area spillway leading from the convergent section of the passage, and operating means for adjusting said diffuser parts to vary the area of said spillway whereby the flow at the diffuser throat may be maintained at only slightly above sonic velocity to enable a substantial de celeration of the flow to occur in the divergent section of the passage.

r 1 l 25. In a ram jet engine, a multi-part diffuser providing a convergent-divergent passage leading to the engine com bustion chamber for reducing the velocity of a fluid stream entering the difiiuser at a supersonic velocity to a subsonic velocity at said combustion chamber, the parts of said diffuser being relatively movable to provide a variable area spillway leading from the divergent section of the passage, andoperating means for adjusting said diffuser parts to vary the area of said spillway whereby the transition from supersonic to subsonic flow may be maintained in the divergent section of the passage near the throat to provide for substantial deceleration of the flow in the divergent section of the passage.

26. A multi-part diffuser providing a convergen -divergent passage leading to a conduit for reducing the velocity of a fluid stream entering the difiuser at a supersonic velocity to a subsonic'veloeity at said conduit, the parts of the difiuser being relatively movable to provide a spillway of variable area leading from the divergent section of the passage, and operating means for adjusting said diffuser parts to vary the area of said spillway whereby the transition from supersonic to subsonic flow may be maintained in the divergent section of the passage near the throat to provide for substantial deceleration of the flow in the divergent section of the passage.

No references cited. 

1. A DIFFUSER FOR REDUCING THE VELOCITY OF A FLUID STREAM FROM A SUPERSONIC VELOCITY AT THE DIFFUSER ENTRANCE TO A SUBSONIC VELOCITY AT THE ENTRANCE OF A CONDUIT, COMPRISING A CONVERGENT-DIVERGENT PASSAGEWAY WITH THE TRAILING EDGE OF THE DIVERGENT SECTION THEREOF SPACED FROM SAID ENTRANCE, A TUBE OF CONVERGENT-DIVERGENT FROM ARRANGED FOR LONGITUDINAL MOVEMENT BETWEEN FIRST AND SECOND POSITIONS WITHIN SAID PASSAGEWAY, SAID TUBE WHEN IN THE FIRST POSITION HAVING THE LEADING EDGE OF THE CONVERGENT SECTION THEREOF SUBSTANTIALLY AT THE THROAT OF THE PASSAGEWAY WHEREBY THE CONVERGENT SECTION OF THE TUBE FROMS A REARWARD CONTINUATION OF THE CONVERGENT SECTION OF THE PASSAGEWAY, AND SAID TUBE WHEN IN THE FIRST POSITION HAVING THE TRAILING EDGE THEREOF AT THE ENTRANCE OF THE CONDUIT WHEREBY THE DIVERGENT SECTION OF THE TUBE FORMS A FORWARD CONTINUATION OF THE CONDUIT, SAID TUBE WHEN IN THE SECOND POSITION HAVING THE LEADING EDGE OF THE CONVERGENT SECTION THEREOF SPACED FROM THE THROAT OF THE PASSAGEWAY TO PROVIDE A FIRST SPILLWAY BETWEEN THE DIVERGENT SECTIONS OF THE TUBE AND PASSAGEWAY, AND SAID TUBE WHEN IN SAID SECOND POSITION HAVING THE TRAILING EDGE OF THE DIVERGENT SECTION THEREOF SPACED FROM THE ENTRANCE OF SAID CONDUIT TO PROVIDE THEREBETWEEN A SECOND SPILLWAY, A SLIDE VALVE ARRANGED FOR LONGITUDINAL MOVEMENT FOR VARYING THE OUTLET AREA OF SAID FIRST SPILLWAY, OPERATING MEANS FOR MOVING THE TUBE AND FOR SIMULTANEOUSLY MOVING SAID SLIDE VALVE TO OPEN AND CLOSE THE LATTER AS THE TUBE IS MOVED TOWARD AND AWAY FROM SAID SECOND POSITION, AND PRESSURE RESPONSIVE MEANS FOR CONTROLLING SAID OPERATING MEANS, SAID MEANS EFFECTING MOVEMENT OF THE TUBE TOWARD SAID FIRST POSITION WHEN THE RATIO OF TOTAL HEAD AT THE TUBE THROAT TO TOTAL HEAD AT THE TUBE OUTLET IS ABOVE A PREDETERMINED VALUE AND FOR EFFECTING MOVEMENT OF THE TUBE TOWARD SAID SECOND POSITION WHEN SAID RATIO IS BELOW SAID VALUE. 